Large-size plastic containers that have a capacity of 1.5 L, 2.0 L, or more, and are used to store tea, alcoholic drinks, and other beverages; condiments; or the like are often fitted with a handle to improve ease of use. For reasons related to performance and cost, such handle-equipped containers are often made from polyethylene terephthalate or another polyester, and the handle material is often made from polypropylene.
The following are examples of handle-equipped plastic containers that are known in the art.    Prior Art Document 1: Japanese Laid-open Patent Application No. 2000-255580    Prior Art Document 2: Japanese Laid-open Patent Application No. 2000-43877
In Prior Art Document 1, the handle is made from the same polyester as the container to aid recyclability. As shown in FIGS. 9 and 10, the container of Prior Art Document 1 comprises a polyester container g, which has a finish part a, a shoulder part b, a body part c, and a base part d in the stated order from the top part; which has a concavity e provided to a portion of the body part c; and which has a handle-attaching convexity f provided to the concavity e; and a polyester handle h, which is attached to the handle-attaching convexity f of the container g. A space j is provided between the handle h and a wall surface i that surrounds the convexity f on the concavity e. As a result, less frictional resistance occurs in the portion provided with the space j between the wall surface i that surrounds the convexity f and the handle h; blow-molding ability improves; no incidence is presented in regard to scratches, melting, or whitening of the concavity e, nor of thickness defects in the concavity e or the base part d; and a satisfactory handle-equipped container can be obtained.
The heat-resistant handle-equipped container according to Prior Art Document 2 is obtained as described below. As shown in FIG. 11, the separate handle h is insert-molded on the body part c of the top part of the container g, and the transverse cross section of the body part c of the top part to which the handle h is attached is molded into a round shape. The transverse cross section of the body part c of the base part, to which a reduced-pressure absorption panel k is attached, is molded into a quadrangular shape, a side wall of the body part c that enfolds an undercut part of the handle h is heat set, and the ratio between the area of the reduced-pressure absorption panel k and the area of the surface below the neck ring of the finish part a is 0.22 or greater. A satisfactory handle-equipped heat-resistant container is thereby obtained.
A large demand has arisen over the past several years for plastic containers having a quadrangularly shaped transverse cross section in order to increase the volumetric efficiency during storage and transport.
The handle-equipped container of Prior Art Document 1 is described as having an effect whereby blow-molding properties are improved, and anomalies arising in the concavity e and base part d are eliminated. However, in the examples, mention is only made of the body part having a round cross-sectional shape, and no mention is made in regard to an object of obtaining an angular handle-equipped container, nor to resolving means. Moreover, no mention is made in regard to the imparting of a heat-resisting property that enables high-temperature filling to be performed.
The body part of the heat-resistant handle-equipped container of Prior Art Document 2 has a quadrangular cross section below the position where the handle is attached; however, the upper part where the handle is attached has a round cross-section, which is inadequate for improving volumetric efficiency. Favorable heat resistance can be obtained by heat-setting the body part that enfolds an undercut part of the handle. However, the heat-setting is performed on the container wall, which contacts the molding mold, and the portion that enfolds the handle undercut part is positioned within the container. Therefore, heat setting cannot be directly performed, and a concern arises in that the strength with which the handle is attached will decline as a result of contraction and deformation during high temperature filling.